Alkali has been long used as a method for stabilization of biosolids. USEPA recommends holding biosolids for a period of time at a pH of 12 or greater as a method for production of stabilized biosolids. Disadvantages of this method include high volumes and high costs of the alkali required to achieve this high pH, the increased emission of ammonia from the biosolids at the higher pH values and limitations on the amounts of high alkali-containing biosolids that may be applied as fertilizer to soils.
Biosolids coming from the wastewater treatment plant typically contains substantial populations of microorganisms including pathogens and one motivation for using alkali to increase the pH is to partially or preferably completely kill these organisms.
The alkali component of the biosolids sludge additionally, and very importantly, acts to preserve the biosolids product by totally preventing or reducing the potential for regrowth of microorganisms in the product.
A principal way in which alkali is used up in biosolids is through hydrolysis.
The prior art shows that to achieve long term stability and, thus long term stability of the pH, while stored of the resulting BSP requires both large amounts of expensive alkali and large amounts of heat applied over an extended period.
With respect to hydrolysis of bio materials it has been said that:                Alkaline hydrolysis is a simple, natural process by which complex molecules are broken down into their constituent building blocks by the insertion of ions of water (H2O), H+, and OH− between the atoms of the bonds that held those building bocks together. The process occurs in nature when animal tissues and carcasses are buried in soil of neutral or alkaline pH. In this case, alkaline hydrolysis is aided by the digestive processes of soil organisms. Alkaline hydrolysis also occurs in our small intestines after we eat; the complex molecules of proteins, fats, and nucleic acids are hydrolyzed with the aid of digestive enzymes that function most efficiently at a slightly alkaline pH (˜pH8.0 to 8.5) . . . .        Chemistry of the Process        Hydrolysis can be catalyzed by enzymes, metal salts, acids, or bases. Bases are typically water solutions of alkali metal hydroxides such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). Heating the reactants dramatically accelerates hydrolysis. Just as proteins, nucleic acids, polymeric carbohydrates, and lipids were made by organisms via the condensation of building blocks, so can they be depolymerized, or unmade, by hydrolysis.        . . . All proteins, regardless of their origin, are destroyed by alkaline hydrolysis . . . .        Effects of Alkaline Hydrolysis on:        Proteins        Alkaline hydrolysis leads to the random breaking of nearly 40% of all peptide bonds in proteins, the major solid constituent of animal cells and tissues.        Lipids        Simple fats consist of three fatty acid chains bound through ester bonds to a molecule of glycerol. During alkaline hydrolysis, all of these ester bonds, as well as the sterol esters and phospholipids of cell secretions and cell membranes, hydrolyze with the consumption of the alkali, producing the sodium and potassium salts of fatty acids, namely soaps . . . .        Carbohydrates        As a group of polymers, carbohydrates are the constituents of cells and tissues most slowly affected by alkaline hydrolysis. Both glycogen, the most common large polymer of glucose in animals, and starch, the most common large polymer of glucose in plants, are immediately solubilized. However, the breakdown of these polymers requires much longer treatment than is required for large intracellular and extracellular polymers. Some large carbohydrate molecules, the 1-4)-linked glycans, such as cellulose, are quite resistant to alkaline hydrolysis, as they are to digestion in the human intestine. On the other hand, cellulosic materials usually occur only in the digestive tracts of grazing animals where, as a rule, they have been macerated and partially digested. Consequently, further degradation, even if slow, usually does not pose a problem . . . . All monosaccharides (simple sugars), such as glucose, galactose, and mannose, are rapidly destroyed by the hot aqueous alkaline solution.        Nucleic Acids        Nucleic acids are large, unbranched, linear polymers held together by phosphodiester bonds, which are similar to the simpler ester bonds of fats but include a phosphate group as part of the bond structure. These ester bonds are also hydrolyzed with consumption of the alkali, rapidly destroying ribonucleic acid (RNA) and more slowly destroying deoxyribonucleic acid (DNA).        Applications of the Alkaline Hydrolysis Process        In addition to its utility for the disposal of routinely generated animal tissues and carcasses, alkaline hydrolysis is particularly useful for the disposal of many difficult-to-handle biologic and biohazardous wastes . . . .        Resource Recycling Versus Waste Disposal        One truly noteworthy point is that while the animal tissues and carcasses may be called “wastes,” the sterile hydrolyzate produced from them by alkaline hydrolysis is no longer a waste but a resource. This undiluted hydrolyzate, a 5%-7% solution of amino acids, small peptides, sugars, soaps, and electrolytes, is a valuable and versatile nutrient source that can be used as fertilizer, either liquid or dried and solid, as an additive to composting systems, or as a feedstock for anaerobic digestion biogas generation plants that produce methane, steam, heat, and electric power. Biodiesel applications for the hydrolyzate are also being actively explored.        Conclusion        We have attempted in this article to illustrate the versatility of alkaline hydrolysis as a process for treatment and disposal of a variety of biologic, biohazardous, and hazardous wastes in a manner that is nonpolluting, more efficient and economical than incineration, and capable of producing secondary beneficial resources. We are certain that as we learn even more about this process, its applications will continue to increase in medical and veterinary research, clinical practice, and education, as well as in other industries that produce significant amounts of biologic waste, and that it will become the standard method for treating such wastes rather than being considered an alternative method to combustion of incineration.        
From this it is apparent that many persons skilled in the art, PSITAs believe that high-heat pH-12 hydrolysis (herein HHpH12 hydrolysis) provides a complete and useful process for the processing of sewage waste into a useful resource. As shown above, many PSITAsbelieve that the overwhelming action of the HHpH12 hydrolysis is a necessary feature when processing ordinary sewage sludge.
Time has shown that this belief leads inevitably to large energy consumption, large scale pressure vessel equipment, and large amounts of the alkali of choice. Namely a costly and time consuming process to set up and carry out over the long periods of production time required for, say, municipal sewage treatment.
Efforts continue to provide an improved useful and acceptable resource from sewage waste without these costs and limitations.
Many have applied the term thermal hydrolysis to this HHpH12 process and it is sometimes defined as:                Thermal hydrolysis is a process used for treating industrial waste, municipal solid waste and sewage.        Description        Thermal hydrolysis is a two-stage process combining high-pressure boiling of waste or sludge followed by a rapid decompression. This combined action sterilizes the sludge and makes it more biodegradable, which improves digestion performance. Sterilization destroys pathogens in the sludge resulting in it exceeding the stringent requirements for land application (agriculture).[1]        In addition, the treatment adjusts the rheology to such an extent that loading rates to sludge anaerobic digesters can be doubled, and also dewaterability of the sludge is significantly improved.        See https://en.wikipedia.org/wiki/Thermal_hydrolysis        
Again, this demonstrates a thorough processing to a sterilized state.
Further, for instance:
U.S. Pat. No. 6,808,636 describes a process whereby an alkali-treated sewage sludge is heated to a temperature less than 100 degrees Celsius and sheared to reduce the viscosity of the sludge, and
U.S. Pat. No. 5,618,442 provides a process and apparatus for treating sewage sludge having the steps of providing sludge at a desired rate, mixing the sludge with at least one alkaline additive at a proportionate rate to the sludge to raise the pH of the mixture to at least a desired level, providing a pasteurization chamber having a means to heat the contents of the chamber, continuously delivering the sludge and alkaline additive mixture to the inlet opening of the pasteurization chamber, heating the pasteurization chamber to maintain a minimum temperature of the sludge and alkaline additive mixture in the pasteurization chamber.
Of note with respect of US'442 is that pasteurization is often defined as an incomplete sterilization with an operative temperature of about 70 degrees Celsius. Common teaching is that higher temperatures are counter-productive to the process and the ultimate end product as they tend to go too far.
An example of a definition of pasteurization which is commonly understood is as follows:                pasteurization        Simple Definition of pasteurization —: a process in which a liquid (such as milk or cream) is heated to a temperature that kills harmful germs and then cooled quickly.        Source: Merriam-Webster's Learner's Dictionary        Full Definition of pasteurization—: partial sterilization of a substance and especially a liquid (as milk) at a temperature and for a period of exposure that destroys objectionable organisms without major chemical alteration of the substance.        See http://www.merriam-webster.com/dictionary/pasteurization        
Pasteurization is thus specifically designed to be incomplete while HhpH is designed with the opposite in mind, i.e. complete to the nth degree.
In these examples of the prior art processes, the use of alkali corresponds with the kind of teaching form the quotations above, ie a heat/alkali combination to break down the complex and uncertain chemistry of active sewage waste. Inevitably, the amount of alkali used is very high, and, thus, the cost of the process is high due to the high cost of the chemical itself.
It is also widely known that the pH of alkaline biosolids sludge drifts downwards over time. This may be explained as follows:
Alkali is well known to promote hydrolysis of organic molecules, including the polysaccharides, proteins and lipids that are considerable components of biosolids. In many hydrolysis reactions the alkali actually participates in and is used up in the hydrolysis reaction.
And since a portion of the total alkali is used up in this way the pH of the remaining sludge becomes reduced. Reduced pH known to be counter productive to the long term stability and storage of the resulting BSP in many cases.
Objects
It is an object of the invention to provide a testing procedure, an industrial process and a BSP product, wherein the rate of utilization of alkali added is reduced, while maintaining a higher and stable pH in the biosolids result.
It is a further object to better preserve the BSP product by reduction of the potential for microbial regrowth to the extent necessary for particular product uses.
It is a still further object to produce a fertilizer product with a greater consistency in the product by reducing its variability with respect to product alkalinity or pH over the period of storage.
It is yet a still further object to provide a procedure to limit the use of alkali in creation of a stable BSP.
The Invention
In accordance with one aspect of the invention a testing procedure, an industrial process and a resulting product are provided whereby sewage sludge is primarily or firstly pre-hydrolysed in whole or in part by means other than alkali. The alkali is then added to the pre-hydrolysed product. The pre-hydrolysed product from step one has a reduced potential for further or continuing hydrolysis and is more effectively stabilized in step 2 as a liquid BSP.
As a result, less of the alkali will be used up in the step 2 further hydrolysis of the pre-hydrolysed product. Consequently, in situations where the amount of alkali is to be reduced from full sterilization or HHpH12 levels, the pH of the BSP product after the step 2 alkali treatment will remain at a higher or sufficiently high level, drop less during storage periods applicable to particular uses and the BSP product will be better preserved against microbial regrowth.
In a preferred embodiment the pre-hydrolysis first step includes thermal hydrolysis and a period of process time at Temperature.
In accordance with a further aspect of the invention a procedure is provided for reducing usage of alkali materials while maintaining and stabilizing sufficiently high pH levels in biosolids-containing product, referred to as BSP in this application, produced from a sewage sludge having a solids content of 10% or more by:                (a) firstly, commencing a first pre-hydrolysing step in the sewage sludge, in whole or in part by means other than alkali, to produce an extended hydrolysis reduction of complex chemicals components of the sludge, and        (b) then, secondly, adding an alkaline hydrolysis agent thereby raising the pH of the sludge and commencing a 2nd hydrolysis reaction but in an amount insufficient to maintain that pH in the BSP over long term storage in the absence of step one of the procedure, and,        (c) providing a timing separation between said commencement of the pre-hydrolysing step and the said adding of said alkaline agent so as to permit the pre-hydrolysis step to continue without high alkali levels and to reduce or eliminate long term degradation of the pH levels in the BSP in storage, and        (d) storing the stabilized BSP for a period of time.        
Further, the first pre-hydrolysing step may be maintained over a first period and primarily or firstly pre-hydrolyse the sewage sludge in whole or in part.
Further, the first pre-hydrolysing step may include a thermal heating step and an optional cooling to/from either 60-80 or 80-125 degrees Celsius to ambient.
In another aspect the invention provides a procedure including a shearing step before the addition of the alkaline hydrolysis agent of step 2.